by Geoff Chester, USNO Public Affairs | 29 May 2024 Messier 51, the "Whirlpool Galaxy" in Canes Venatici, imaged 2024 May 25 from Mollusk, Virginia with a ZWO Seestar S50 "smart telescope" The Moon wanes in the morning sky this week, turning northward along the ecliptic as she wends her way through autumn’s rising constellations. Last Quarter occurs on the 30th at 1:13 pm Eastern Daylight Time. Look for Luna just over a degree southeast of yellow-tinted Saturn before dawn on the morning of the 31st. You will find the Moon flanking ruddy Mars in morning twilight on the mornings of June 2nd and 3rd. The June citizen-science Globe at Night campaign begins on the 28th and lasts through June 6th. The target constellation for this period is Boötes, the Herdsman, whose brightest star Arcturus dominates the evening and late night hours. While Arcturus is the brightest star in the northern sky, the rest of the constellation is a bit harder to trace out under urban skies. Only two of the other stars in Boötes are brighter than third magnitude, so you will want to get out into more rural areas to see the constellation’s shape. The basic outline of the Herdsman resembles an ice cream cone, with Arcturus marking the cone’s tip. The top of the cone, where the scoop of ice cream sits, occupies the space just above the “arc” from the handle of the Big Dipper to Arcturus. Once you have identified the constellation, compare your view with the charts on the Globe at Night web app to make your observation. The second-brightest star in Boötes is called Izar, and it is a wonderful target for owners of small telescopes. Initially you will see a single, bright yellow colored star, but with higher magnification and steady air, it resolves into a lovely pair of blue and gold stars. Its double nature was discovered in 1829 by the Baltic astronomer Friedrich G.W. Struve, who bestowed the flowery moniker “Pulcherrima” on the star as a descriptor of its visual beauty. About 10 degrees to the east of Izar is a star of similar brightness, Alphecca, which sits in a small arc of third- and fourth-magnitude stars. This diminutive group is called Corona Borealis, and it has represented a crown of tiara since ancient times. To the Greeks it was a gift given to the Cretan princess Ariadne by the god Dionysus. Despite its obscurity it was one of the 48 constellations identified by Ptolemy, and it appears in the sky lore of many cultures. As with many constellations, it contains a variety of star types, including one of the most spectacular examples of a peculiar type called a “recurrent nova”. T Coronae Borealis is normally a 10th magnitude star, visible only in telescopes. It consists of a cool red giant star that orbits close to a hot white dwarf companion. Periodically matter siphoned from the giant star pools on the surface of the dwarf star. When enough material accumulates, it causes the white dwarf to dramatically flare, and for a few days it will outshine Alphecca before gradually fading. The cycle has a recurrence period of about 80 years, and it is expected to flare again sometime between now and September. Watch this space! Many of you may have seen a popular news item late last week touting a “rare six planet alignment” set to occur on June 3rd. This phenomenon might be visible to astronauts on the International Space Station if they use their telescope, but for us Earthbound viewers the spectacle will be something of a dud. You should be able to see Saturn and Mars as morning twilight gathers, and the waning Moon will wend her way between them as June opens, offering nice photo opportunities on the mornings of June 1st through the 4th. As for the other planets, Neptune is visible with a telescope between Saturn and Mars, while Uranus, Mercury, and Jupiter will be lost in the gathering twilight glare.